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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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  <body>
    <script>
      let arr = [2,5,10,22,55,10,52,88,59]
      let flag = 0
      for(let i=0;i<arr.length;i++){
        if(arr[i]===10){
          document.write(`10的下标是${i}<br>`)
          flag=1
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      if(flag===0){
        document.write(-1)
      }
    </script>
  </body>
</html>